The output shaft of some drive units is intended to occupy an exactly defined rest position within a particular range of tolerances. This is for example also applicable to windshield wiper systems in which the wiper blade is to be parked as closely to the rim of the windshield as possible. As far as wiper blades are concerned which are driven by an electric motor, in a customary way the electric motor is braked by short circuit, when the wiper blades enter the rest position. This electric-dynamic brake does not always effect a satisfactory rest position. This rest position is rather also considerably dependent on the battery voltage and/or on the condition of the windshield. The play between the individual gear members nearly always existing contributes also to the fact that the desired rest position is not always occupied. The gearing play has effects as well that during operation the reversing positions of the wiper blade are not exactly maintained.
In a windshield wiper system known from the laid open German printed specification 3 514 199 it has been attempted to solve the above mentioned problem by limiting the pendulum angle of the output shaft by a stop on the pinion connected with the output shaft in a manner protected against twisting and by a counterstop fixed on the housing in any direction of rotation. The pinion thereby has a tooth gap and the two teeth adjacent to the gap co-operate with the counterstops by means of a linearly displaceable pressure-transmitter.
From the German laid open printed specification 3 740 312 a windshield wiper system is also known in which the pendulum angle of the output shaft is to be limited by stops for the pinion. In this windshield wiper system a pin is pressed into a bore of the pinion which pin protrudes axially over one side of the pinion, runs to and fro in a groove of the gear housing and in the reversing positions of the wiper blade abuts on rubber segments inserted into the groove of the gear housing. The pin can be designated stop member, by which the pendulum angle of the output shaft is limited.